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Examination of the Thermal Conditions of a Wood Floor Assembly above a Compartment Fire

Four real-scale experiments were conducted by the National Institute of Standards and Technology to measure the temperatures above and below a wood floor assembly exposed to fire conditions from below. The objectives of the experiments were: 1) to examine the heat transfer through a wood floor assembly and 2) to examine the ability of a thermal imager to determine the potential severity of the fire beneath the floor assembly and the ability to provide a sense of the structural integrity of the floor assembly in order to provide improved situational awareness.

Gas temperatures of the upper and lower compartments as well as the surface temperatures of the floor assembly were measured with thermocouples (TCs). Three commercially available thermal imagers (TIs), each with a different type of sensor were used to view and record the thermal conditions of the top of the floor assembly from the open doorway in the upper compartment. Times to collapse of each floor were also noted. Given the insulating effects of the OSB and the floor coverings, the temperature increase or thermal signatures viewed by the TIs were small given the fact that the ceiling temperatures below the OSB were in excess of 600 ºC (1112 ºF).

These experiments demonstrated that TIs alone cannot be relied upon to determine the structural integrity of a wood floor system. Therefore, it is critical for the fire service to review their practice of size-up and other fire ground tactics needed to enable the location of the fire prior to conducting fire operations inside a building. The United States Fire Administration (USFA) provided support for this project.

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Structural Collapse Fire Tests: Single Story, Wood Frame Structures

A series of fire tests was conducted in Phoenix, Arizona to collect data for a project examining the feasibility of predicting structural collapse. The fire test scenario was selected as part of a training video being prepared by the Phoenix, Arizona Fire Department. Multiple fires were started in each structure to facilitate collapse; the fires were not intended to test the fire endurance of the structures. Four structures with different roof constructions were used for the fire tests. Temperatures were measured as a function of time in four locations within each structure. Furniture items were placed in the front and back of each structure to simulate living room and bedroom areas. The living room and bedroom areas of each structure were ignited simultaneously using electric matches. Peak temperatures obtained during the tests ranged from approximately 800 °C (1500 °F) to 1000 °C (1800 °F). The roof of each structure collapsed approximately 17 minutes after ignition. In addition to the full scale tests, the plywood and oriented strand board (OSB) roofing materials were tested using a cone calorimeter to characterize the fire properties of the materials.

Two fire tests were conducted in a warehouse located in Phoenix, Arizona to develop data for evaluation of a methodology for predicting structural collapse. A firewall was constructed to divide the warehouse into two fire compartments. Temperatures were measured as a function of time in three locations during the first test and in two locations during the second test. In addition, the volume fraction of carbon monoxide was measured at selected locations during each test. Stacks of wood pallets were used as the primary fuel source and were ignited using paper and an electric match. Some combustible debris and the building structural elements provided the remainder of the fuel load. Peak temperatures obtained at different elevations ranged from approximately 300 °C (570 °F) to 800 °C (1470 °F). Peak carbon monoxide volume fraction reached 4 % in the first test and 5 % during the second test. The roof of the front half of the structure burned through approximately 18 min after ignition of the fire for the first test. The roof of the back half of the structure burned through about 15 min after the start of the second test.

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Trends in Firefighter Fatalities Due to Structural Collapse, 1979-2002

Between the years 1979 and 2002 there were over 180 firefighter fatalities due to structural collapse, not including those firefighters lost in 2001 in the collapse of the World Trade Center Towers. Structural collapse is an insidious problem within the fire fighting community. It often occurs without warning and can easily cause multiple fatalities.

As part of a larger research program to help reduce firefighter injuries and fatalities the U.S. Fire Administration (USFA) funded the National Institute of Standards and Technology (NIST) to examine records and determine if there were any trends and/or patterns that could be detected in firefighter fatalities due to structural collapse. If so, these trends could be brought immediately to the attention of training officers and incident commanders and investigated further to determine probable causes.

REPORT

Collapse Prediction Technology

A field-based monitoring technique that utilizes measurements of fire-induced vibration was developed and first demonstrated under a previously funded research effort. This report details the findings of the ensuing 3-year endeavor in which significant improvements were made to both field-test and analysis procedures. A real-time monitoring tool has been developed and numerous full-scale burn tests on a variety of structures have been completed. A significant contribution of the research stems from the use of system stability theory to aid in the interpretation of the field measurements. The techniques described in this report can be used to monitor burning structures and to provide visual indicators that track changes in structural stability.